Both n-type chalcogenide materials and/or p-type chalcogenide materials have photovoltaic functionality (also referred to herein photoabsorbing functionality). These materials absorb incident light and generate an electric output when incorporated into a photovoltaic device. Consequently, these chalcogenide-based photoabsorbing materials have been used as the photovoltaic absorber region in functioning photovoltaic devices. Illustrative p-type chalcogenide materials often include sulfides, selenides, and/or tellurides of at least one or more of copper (Cu), indium (In), gallium (Ga), and/or aluminum. Although specific chalcogenide compositions may be referred to by acronyms such as CIS, CISS, CIGS, CIGST, CIGSAT, and/or CIGSS compositions, or the like, the term “CIGS” shall hereinafter refer to all chalcogenide compositions and/or all precursors thereof unless otherwise expressly noted.
It is known that these chalcogenide films can be made by sputtering one or more of the components onto an appropriate substrate potentially followed by chalcogenization. For example, Britting et al, “Development of Novel Target Materials for Cu(In, Ga)Se-Based Solar Cells”, Plasma Process. Polym. 2009. 6 teaches about the formation of sputter targets having a ternary copper, indium, and gallium phase via casting.
As sputter targets are used, there are areas that are sputtered away more quickly than other areas, resulting in what is commonly known as a “racetrack” groove. Planar geometry targets demonstrate this behavior clearly, with only approximately 20-50% of the material actually removed during sputter deposition from the start to end of life to the target, with the end of life defined as when the deepest part of the racetrack groove penetrates the full target thickness down to the target bonding or backing plate. This percentage is determined by the specific magnetron style and target construction. Rotatable geometry targets demonstrate a “racetrack” consisting of most of the exposed target material, with an additional pronounced racetrack groove near the two ends of the targets, which can also leave a significant amount of alloy behind, although less than the case for the planar targets, with approximately 70-90% of the target material removed during the sputter process.